1. Field of the Invention
This invention relates to semiconductor wafer handling apparatuses and methods, and more particularly to the use of an apparatus to prevent damage to wafers.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
During the fabrication of semiconductor devices, semiconductor wafers may be subjected to several processes. Such processes may include, but are not limited to, anneals, depositions, diffusions, thermal oxidations, ion implantations, and etches. Generally, these processes are performed sequentially and therefore, the cycle time of a finished device may be quite lengthy. For example, the cycle time for fabricating some devices may be several days or weeks. As such, mass production methods may be required to meet production needs. Consequently, batch-production techniques may be incorporated into semiconductor fabrication processes in order to simultaneously process multiple wafers. In addition to increasing production, the used of batch production methods may include an improved economy of scale. In particular, a reduction in per unit cost may be realized through increased operational efficiencies.
Another advantage of incorporating batch production techniques is the ability to more closely monitor quality and process control parameters. The increased number of wafers processed may offer valuable information regarding the process variables and/or equipment. As such, periodic inspections of the wafers may be performed between one or more of the fabrication steps. These inspections may be used as a means of monitoring quality control, which is essential for maintaining high manufacturing yields in fabrication. For example, the inspections may be helpful in identifying defects or determining if design specifications have been met. Consequently, equipment and/or processing parameters may be adjusted in response to the inspection results in order to reduce the occurrence of defects and/or meet design specifications of the device.
In a batch production process, multiple wafers may be processed through a series of fabrication steps without interruption. Alternatively, the wafers may be stored between fabrication steps until inspection or further processing is necessary. In either case, the wafers may be transported and/or stored in wafer cassettes or wafer carriers (hereafter called xe2x80x9cwafer cassettesxe2x80x9d). In general, wafer cassettes are any supporting structure used to contain or transport wafers or substrates. Wafer cassettes usually consist of an array of narrow slots that are closely situated. Each slot is generally designed to contain a single wafer. In addition, a portion of each slot may provide access for loading and unloading wafers. In some cases, wafer cassettes may be designed to load and unload wafers either horizontally or vertically. Such load and unload operations may be necessary for periodic inspections as discussed above.
As with many wafer handling processes, however, unloading and loading wafers into cassettes may cause damage to the wafers. Such damage may render one or more devices upon a wafer unusable, thereby reducing production yield and increasing manufacturing cost. One substantial cause of wafer damage stems from the insertion of wafers into the narrow slots of the cassette. Due to several factors, including the thinness of the wafers and the close proximity of the slots, it is likely that a wafer may be incorrectly inserted into the cassette. For example, a wafer could be inadvertently placed into an occupied slot. The placement of a wafer into an occupied slot may likely cause damage to both the wafer being inserted and to the wafer residing in the slot. It would, therefore, be desirable to develop a system and method to prevent damage to wafers while inserting a wafer into a cassette.
The problems outlined above are in large part addressed by a system and method for preventing damage to wafers arranged in a wafer cassette. In particular, an apparatus is provided to protect wafers arranged in a wafer cassette during insertion of a wafer into the cassette. In one embodiment, the apparatus may be a separate entity from the wafer cassette. In this manner, the apparatus may be situated about the cassette such that the wafers arranged in the cassette are protected during insertion of a wafer. In one embodiment, the apparatus may be an attachable component of the wafer cassette. As such, the apparatus may be adapted to fit on various configurations of wafer cassettes. In another embodiment, the wafer cassette itself may be adapted to at least partially cover and protect the wafers arranged in the cassette during insertion of a wafer. Consequently, a method is provided using either embodiment of the apparatus. In particular, the method may include inserting a wafer into a wafer cassette by shielding one or more slots of the cassette, exposing a designated slot of the cassette, and inserting a wafer into the designated slot.
The apparatus may be further adapted to ensure the wafer is placed into a designated slot in the cassette. In one embodiment, such a placement may be achieved by using a shield with an opening that exposes the designated slot. Consequently, the apparatus may include a shield with an opening that partially covers the wafers and exposes the designated slot prior to inserting the wafer into the cassette. Preferably, the shield spans at least three consecutive wafer slots of the cassette. In some embodiments, the opening in the shield may be tapered such that a portion of a wafer slot adjacent to the designated slot may be exposed prior to inserting the wafer into the cassette. Furthermore, the opening may be fixed within the shield. In such an embodiment, the apparatus may be adapted to allow movement of the shield across a length of the cassette. In addition or alternatively, the apparatus may be adapted to allow movement of the shield across a width of the cassette. In another embodiment, the shield may be fixed within the apparatus. Consequently, the shield may be adapted to allow movement of the opening across the length of the cassette.
In an alternative embodiment, the apparatus may include multiple shields. In particular, each of the shields may be adapted to cover a respective single slot of the cassette. In some cases, the apparatus may be adapted to displace a shield covering a designated slot prior to inserting the wafer into the cassette. In this manner, the apparatus may be adapted to allow movement of the shields across a length of the cassette. In addition or alternatively, the apparatus may be adapted to allow movement of the shields across a width of the cassette. In some embodiments, the apparatus may further include a frame adapted to maintain the shields in close proximity to the wafer slots. For example, the shields may attach to the frame. In other embodiments, the frame may be adapted to allow the shields to move within the frame. More specifically, the frame may be adapted to allow the shields to move across the width and/or the length of the apparatus.
In an alternative embodiment, the apparatus as described herein may include a wafer cassette adapted to at least partially cover and protect wafers arranged in the cassette during insertion of a wafer. Such a cassette may include one or more shields. In such an embodiment, the wafer cassette itself may prevent damage to wafers arranged within the cassette during the insertion of a wafer in a similar manner as described for the apparatus mentioned above. As such, the cassette may be adapted to prevent a wafer from being inserted into occupied wafer slots of the cassette. The cassette may further include a frame adapted to maintain one or more of the shields in close proximity of an array of wafer slots within the cassette. In some embodiments, the frame and shields may be a fixed portion of the cassette. Alternatively, the frame and/or shields may be detachable components of the cassette. In addition, the shields may span at least three consecutive wafer slots and provide an opening that partially covers the wafers and exposes a designated slot of the cassette prior to inserting a wafer. Alternatively, each of the shields may be adapted to cover a respective single slot of the cassette. In some embodiments, the wafer cassette may include a mechanism that positions the shields over the slots. Such a system may allow a designated slot of the cassette to be exposed. For example, in an embodiment in which the cassette includes a shield with an opening, the frame may be adapted to orientate the shield such that the opening is over the designated slot. Alternatively, in an embodiment in which the cassette includes multiple shields adapted to cover a respective single slot, the frame may be adapted to allow displacement of the shields to expose the designated slot.
A method for inserting a wafer into a wafer cassette is also contemplated herein. Such a method may include shielding one or more slots of a cassette, exposing a designated slot absent the shielding, and inserting a wafer into the designated slot. Shielding the slots may include placing a shield with an opening over the slots. In such an embodiment, exposing may include positioning the opening over a designated slot, thereby covering the slots adjacent to the designated slot. Alternatively, shielding may include placing multiple shields, each over respective single slots of the cassette. Consequently, exposing may include displacing a shield placed over the designated slot of the cassette.
Several advantages may be realized from the devices and methods contemplated herein. For example, shielding a wafer from being inserted into an occupied wafer slot may prevent damage to both the wafer in the slot and the wafer being inserted. Consequently, the likelihood of damaging wafers may be reduced and an increase in production yield and a decrease in fabrications costs may be realized. In addition, the apparatuses and methods as described herein may allow a wafer to placed into a designated slot a faster rate since an opening in the shield may guide the placement of a wafer into the designated slot. As such, less time may be needed to load and unload a wafer cassette, thereby reducing the time to process the wafers.